Yes, MONOPOLIES is a Scrabble word!

Letter values in Scrabble US: M 3, O 1, N 1, O 1, P 3, O 1, L 1, I 1, E 1, S 1.

Is it a valid word?

MONOPOLIES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

(economics) a market in which there are many buyers but only one seller
exclusive control or possession of something
a board game in which players try to gain a monopoly on real estate as pieces advance around the board according to the throw of a die